Creating Multimedia Presentation based on Constraint Satisfaction Problems in Multimedia Databases Masayo Kaji Department of Computer and System Engineering, Graduate School of Science and Technology, Kobe University
[email protected] Kuniaki Uehara Research Center for Urban Safety and Security, Kobe University
[email protected]
Abstract We have studied a mechanism for creating multimedia presentation from various multimedia objects such as video and image. The important problem for creating multimedia presentation is temporal composition relations among multimedia objects. Temporal relations specify the ow of multimedia presentations in space and time, and the way that multimedia presentations handle the events that occur in the context. We should consider both syntactic and semantic aspects in creating multimedia presentation. Syntactic aspect means how the multimedia objects are scheduled. Graph model indicates visually temporal relation between multimedia objects, and can simulates the multimedia presentation in advance. This simulation can detect contradictions between temporal relations and con guration errors. Semantic aspect corresponds to the presentation constraints. Presentation constraints occur when user-speci ed presentation is played out because users may have various requirements. In this paper, we propose the way to create multimedia presentation so as to satisfy the constraints between multimedia objects.
1 Introduction With the availability of enormous digitized multimedia contents from WWW, satellite digital broadcasting, CATV, and so on, multimedia database systems have become important increasingly. WWW o ers the general public broad access to digital contents in everyday communication. Digital broadcasting and CATV
have made remarkable progress and provides various kinds of information. In that, they act as huge shared databases of multimedia contents, and the typical leaders of multimedia contents providers. In these network services, people can download multimedia information, and record the data on storage. Moreover, they can compose and share multimedia information consisting of fragments of multimedia data stored in a large multimedia database. For example, people can arrange certain HTML document into new their own speci ed page. The text data is reconstructed easily according to users' tastes, but it is very diÆcult for ordinary people to edit multimedia presentation. Therefore, our research supports the editing, arrangement, or composition of multimedia presentation. A multimedia database contains various data, such as video, audio, text, and image. The data structure should support both text-based data and continuous data streams. We consider such data as multimedia objects so that the model of multimedia objects needs to express them. In order to represent the multimedia objects, the time ow of applications becomes a critical part of the model. Speci cation models for multimedia objects put emphasis on temporal aspects. Most of speci cation models are based on Allen's relations [1]. Allen de ned seven basic relations between two temporal intervals. For example, a TV program starts at 9:00pm, and nishes 11:00pm. The TV program can be considered as one of multimedia objects. In addition, \interval" is considered as a range from 9:00pm to 11:00pm, and \duration" as two hours.
Allen's relations require this duration of the interval. Before designing the speci cation model, interval duration must be known. This means that multimedia database systems must determine duration of multimedia objects, because presentations are almost dependent of duration. Users have various requirements for multimedia presentation. For example, people may watch soccer game on TV. Highlights scenes of the game are sometimes replayed though the game continues. They may want to watch the game with highlight scenes. In this case, both a live broadcast of soccer game and highlights scenes are played out at the same time. As regard to each video, each size of window, and desktop layout are necessary to keep users' attentions. In this way, users may arrange another di erent presentation from a certain video. We consider the arrangement of multimedia data as multimedia presentation. In creating multimedia presentation, we should consider both syntactic and semantic aspects. Syntactic aspect means how the contents are scheduled. Graphical model, that is petri net, can capture the relation between multimedia objects, and provide simulation of presentation. We can attempt the organization of multimedia presentation because petri net can show the time ow of multimedia objects visually. That is why we use petri net for order of multimedia objects. Semantic aspect represents the presentation contents. Presentation constraints exist when userspeci ed presentation is play out. Therefore, we will introduce constraint satisfaction problems [2] into creating scenario temporal speci cation, and userspeci ed presentation. In this paper, we develop a multimedia database system as a tool to extract and create presentations from multimedia contents with putting emphasis on the constraints between multimedia objects. Section 2 considers that multimedia objects are scheduled in good ordering. Section 3 presents multimedia objects expression for modeling by using scenario speci cation. In section 4, we introduce petri net and a graphical user interface of our multimedia database system. In section 5 describes the way of constraint satisfaction problems.
details. In this case, both studio video, where an anchorperson presents the news, and live video can be played for the presentation as parallel streams, which can shorten the time of news video. In this way, users may desire variable presentations because they have di erent aims and di erent available environments on each desktop. According to users' requests, the system has some restrictions: the playing time, the number of monitor windows, the overlap of audio, and so on. If some videos are played at the same time, some audios are overlapped. Therefore, coordination for multimedia objects (video, audio, image, and text) is very important thing to create presentation. That is, we should create multimedia presentation that multimedia objects are scheduled in cooperation. We consider the six requirements when users see multimedia presentation. The time length of the presentation (t). The number of parallel monitor windows wi (i = 1; : : : ; n). An upper bound is n. Audio overlapped. Size of monitor windows on the screen. Each window has height (heighti ) and width (widthi ), where i(i = 1; : : : ; n) is the number of windows. Layout on the screen. Focus window among monitor windows. For example, users can watch two videos and an image le simultaneously. In this case, they determine an upper bound on the number of parallel monitor window to n = 3. Screen W2 height
W1 W3
width
Monitor Window
Focus Window
W1 W2 W3
W1
2 Coordination for Multimedia Objects
Figure 1: Multimedia Presentation.
Contents and organization of presentation vary depending on available resources, purpose, and so on. Let us consider the case that people want to watch a long news video, but they have little time to do so. Some may want a video, which tells outline contents in a short time. Others may want one, which tells a
Thus, we construct a user-speci ed presentation considering the selection of multimedia objects, the scheduling of them, and the playing presentations to the users. We should develop the system that solves all constraints between multimedia objects. The way of presentation generation is two steps. First, editors
describe scenario temporal speci cation. As the second step, the system automatically creates presentation from designed scenario temporal speci cation by satisfying some requirements.
3 Representation of Multimedia Objects Before constructing the presentation, a suitable data model is required. We need to model multimedia information such that we can maintain both structural and content information. Many existing models of multimedia objects consider their spatial and temporal domains [3]. We use the model that emphasis is placed on the temporal domain because an important part of modeling is that all multimedia objects are ordered on the time ow. In some temporal models, Allen's relations are adopted as the representation of multimedia objects. In Allen's relations, it is necessary to de ne the temporal intervals. A temporal interval is de ned by two temporal instants: the start and the end of objects. Seven basic relations between two temporal intervals are before, meet, during, start, nish, overlap, and equal. Scenario temporal speci cation [4] makes use of Allen's relations for temporal relations. We use scenario temporal speci cation as descriptions for the time ow of multimedia objects. Scenario temporal speci cation consists of three parts: declarations, assigns, and relations. For example: declarations of multimedia objects such as video, audio, and text. The duration means play-out time of each object. multimedia-object(duration):TYPE; assigns the object to resource. We de ne a resource as a le name for the multimedia-object. assigns(multimedia-object, \resource"); relations between multimedia objects by using temporal relations. We must specify duration parameter if required. multimedia-object:= temporal-relation(multimedia-object1, multimedia-object2 [,duration]); Let us consider an example of scenario temporal speci cation. Multimedia objects are two text les, image, and three video streams. For example, text les include news contents, image is a picture, and video streams are movies. In studio, an anchorperson presents news and the simple news content is shown on TV screen. Because the simple content disappears at once, it showed as a text le \Text1" in multimedia presentation. Text1 and studio video Video1 are played at the same time in our speci ed presentation.
In the same way, we design scenario the follows:
*declaration Text1(4):TEXT; Text2(43):TEXT; Image1(2):IMAGE; Video1(20):VIDEO; Video2(45):VIDEO; Video3(15):VIDEO
*assign assign(Text1, \text1.txt"); assign(Text2, \text2.txt"); assign(Image1, \image1.gif"); assign(Video1, \video1.mv"); assign(Video2, \video2.mv"); assign(Video3, \video3.mv");
*relation StudioVideo := nish(Text1, Video1, 16); LiveVideo1 := start(Text2, Video2); LiveVideo2 := meet(Image1, Video3); LiveVideo := during(LiveVideo1, LiveVideo2, 22); newsVideo := meet(StudioVideo, LiveVideo);
In Figure 2, some multimedia objects are scheduled by temporal relations. In this way, scenario temporal speci cation can represent the temporal composition of multimedia objects. Studio Video Video1
Live Video Image1
Text1
Video3 Text2 Video2
0
20
65 Time(sec.)
Figure 2: The Order of Multimedia Objects.
4 The Use of Scenario Temporal Speci cation We use scenario temporal speci cation for model of presentation. In order to visualize this scenario temporal speci cation, we will introduce the concept of petri net. Moreover, we show our graphical interface to design scenario temporal speci cation easily.
4.1 Petri Net Allen's relations have the problem that multimedia objects expressions are dependent of multimedia objects duration. The temporal relations are designed to
specify relations between multimedia objects of determined duration. Therefore, they are not appropriate for undetermined duration. If creators produce a video digest from several multimedia objects, they need to modify the temporal relations between multimedia objects after the change of their duration. In order to solve this problem, the system should represent relations between multimedia objects with unknown duration. We must study the model of temporal relations independent of duration changes. Petri net is one of graph representations. Petri net has some characteristics: (1) petri net considers multimedia objects with known or unknown duration, and (2) the simulation of the scenario may detect errors. Let us consider each feature. If a user changes the duration of multimedia object, the system would update it and generate appropriate petri net automatically. A relation takes two multimedia objects as arguments. In Figure 3, meet(object A, object B) means that object B follows object A . Finish(object A, object B, d) means that object B plays and after d object A plays. By using petri net, the system will determine the delay \d" automatically. If object A and object B have di erent duration and they nish at the same time, di erence between their duration is \delay." Where the duration of ObjectA is 20 seconds, and Object B is 35 seconds, delay is 15 seconds if two objects nish at once. d object A
object A
object B
object B
meet(object A, object B)
finish(object A, object B, d)
Figure 3: Examples of Petri Net with Allen's Relations. We adopt petri net as the visualization of scenario temporal speci cation. Djeraba et.al have proposed the mechanism that petri net can simulate the scenario and detect three types of errors: speci cation error, graph design error, and allocation resources error [4]. However, graph design error and allocation resources error are meaningless errors when presentation is created. Therefore, we will de ne new errors \graph con guration error"and \duplicate allocation error." First, We explain speci cation error. Next, we explain our errors comparing with graph design error and allocation resources error. Speci cation error is that two multimedia objects are declared with di erent duration, and linked by temporal relation equal. In Figure 4, duration of object1 is 10, and object2 is 40. Though they have di er-
ent duration, they are speci ed by \equal" of temporal relations.
Speci cation error object1(10):VIDEO; object2(30):VIDEO; equal(object1, object2); duration=10 object6 duration=30 object7
0
10
20
30
Time
Figure 4: The Duration Di erence Between Two Objects. Secondly, graph design error is that multimedia object is declared, but petri net never uses it. However, declared multimedia objects are not used to create petri net because users may select multimedia objects their own way. We de ne graph con guration error that several clusters are not connected by temporal relation.
Graph con guration error object3(10):VIDEO; object4:IMAGE; object5(20):VIDEO; object6(15):TEXT; object7(16):VIDEO; Video1 := meet(object3, object4); Video2 := start(object5, object6);
For example, users want to select four multimedia objects (object3, object4, object5, and object6) from ve objects (object3, object4, object5, object6, and object7) to design scenario. They may relate object3 with object4 by temporal relations meet, and object5 and object6 are related by start. However, they separate each other (see Figure 5). This example must have a de nition temporal-relation(Video1, Video2). object 5 object3
object4
object 6
meet(object 3, object 4)
start(object 5, object 6)
Figure 5: Graph Con guration Error. In addition, allocation resources error is that the same resources are allocated to several multimedia objects. However, these errors are not so appropriate for
scenario speci cations. Allocation resources error may sometimes occur in scenario generation.
Allocation resources error assign(object7, \Video1.mv"); assign(object8, \Video1.mv");
For example, people sometimes watch a TV commercial that a trade name appears at the start and end of the commercial. Let a trade name shot be a resource \Video1.mv," and object7 be a start shot, and object8 be an end shot. We may allocate \Video1.mv" to both objects. Because this case may sometimes occur in scenario generation, this allocation resources error is not used for simulation of presentation. Therefore, we de ne a new allocation resources error that several resources are allocated to one multimedia object. Examples are the following relation:
Duplicate allocation error
The system allocates the two di erent resources \Video2.mv" and \Video3.mv" to the same multimedia object object9. In this case, the system can not play both \Video2.mv" and \Video3.mv" as one resource. Figure 6 shows an example of petri net generated from scenario temporal speci cation we described in section 3 (see Figure 2). Petri net represents various components of multimedia objects as nodes and describes their inter-relationships in the form of transitions. Video1
t1
t3
t4
Image1
Video3
t5
t8
End
d2 Text2 t2
t6
d1
d3 Text1
Our system can determine the relations directly with graphical user interface. Although Allen de nes seven relations, we use thirteen possible primitive relations between object A and object B. These relations are Allen's relations (before, meet, during, start, nish, overlap), the symmetric counterparts to these six relations, and equal. The symmetric counterparts mean that object A is replaced with object B in Allen's relations. These thirteen primitives are able to represent by four pairwise relationships between the start and the ends of each object, A and B : StartA-StartB, EndA-EndB, EndA-StartB, and StartA-EndA [6]. Figure 7 shows graphical user interface of our system to generate scenario temporal speci cation. Editors determine the combination of the start and the ends by the thumbed slider query lters. The thumbs are manipulated to select the start-points and endpoints. Thumbs for ObjectA and ObjectB
Slider of StartA for ObjectA
assign(object9, \Video2.mv"); assign(object9, \Video3.mv");
Start
4.2 Direct Operation of the Graphical User Interface
t7 d4
Video2
Delay Multimedia Object Time Flow
Figure 6: Petri Net.
Scenario Temporal Specification
Figure 7: Graphical User Interface of Our System. Let us consider the relation between object A and object B. Figure 8 shows a relation of meet(object A, object B). Slider of StartA in the rst (StartA-StartB) thumb is the left of thumb because object A starts earlier than object B. The ending point of object A and the starting point of object B occur at the same time, and the third query is placed at the center of the thumbs as \EndA equals StartB." This means object A and object B is played sequentially by de nition meet(object A, object B). StartA
EndA
objectB StartB
In Figure 6, multimedia objects such as Video1, Text1 are nodes, ft1 ; : : : ; t8 g are transitions, and fd1 ; : : : ; d4 g are delays. For example, we consider Video1 as 40 seconds movie, Text1 as 30 seconds play out. The system will determine d1 as 10 seconds automatically. This means that Video1 is played, and 10 seconds later Text1 is displayed on the desktop.
objectA
EndB
Figure 8: An Example of Temporal Relations meet. By using this graphical user interface, editors create scenario temporal speci cation as follows:
*relations
Scene1 := before(Video1, Text1, 10); Scene2 := start(Video2, Image1,5); Scene3 := meet(Scene1, Scene2);
Thus, users determine the combination of the start and ends by the thumbed slider with easy manipulation, and system determines temporal relations in scenario temporal speci cation. Therefore, even a naive user can create a part of scenario and understand what objects are scheduled owing to simple manipulation.
5 Creating Presentation We propose the organization of multimedia presentation considering various requirements. We incorporate the idea of arti cial intelligence to satisfy some requirements user have.
5.1 Presentation Constraints We have constraints in creating multimedia presentations. Multimedia objects cooperate according to the contents of them, spatial and temporal domain, priority, and so on. Let us consider one of presentation constraints. In Figure 9, Image1 is news title with background music, Video2 is an anchor person scene, and Video3 is a live scene. Because they are overlapped at the time t, we consider \audio" of the presentation constraint at the time t. Video2 Image1
are played simultaneously. Either Video2 or Video3 is played with music of Image1, and Video2 and Video3 must not be played at once. In this way, presentation constraints appear and we should solve this problem to satisfy constraints like audio.
5.2 Constraint Satisfaction Problems Constraint satisfaction problem (CSP) is one of basic technologies in arti cial intelligence. It involves nding combinations of values for problem variables that are consistent with all the constraints. Simple examples used to illustrate CSP are map coloring, scheduling, layout, and so on. A simple CSP consists of a nite set of variable Xi , a domain Di for each variable, and a set of constraints fC1 ; : : : ; Cm g.
Variables: X = fX1; X2 ; X3 g Domain: D1 = D2 = D3 = fa; b; c; dg = D Constraints: pi : Xi 2 D(i = 1; : : : ; 3), : (X1 ; X2 ) 2 f(a; b); (b; a); (b; d)g, : (X2 ; X3 ) 2 f(a; c); (a; d); (b; d)g, p31 : (X3 ; X1 ) 2 f(a; d); (b; b); (b; c)g p12 p23
The solution of this example is (X1 ; X2 ; X3 ) = (a; b; d), (b; a; c). If X1 is de ned a by constraint p12 , X2 is b and X3 is d by the third element (b; d) of constraint p23 . Moreover, constraint p31 includes the value set (a; d) of (X3 ; X1 ). Thus, CSP nds the solutions, which are consistent to all constraints. CSP can represent variables as nodes and constraints as arc, and it is equal to graph representation. This graph is called constraint network. CSP can be used as for the size of window as well by determining a domain a set of discrete value (1, 2,...).
Video3 X1
t
Time(sec.)
p12 : {(a, b), (b, a), (b, d)}
Figure 9: Presentation Constraint among Multimedia Objects.
X2
p31 : {(a, d), (b, b), (b, c)}
X3
p23 : {(a, c), (a, d), (b, d)}
These multimedia objects would include some elements: play (a), not play (b), only music (c), only speech (d), music and speech (e), and no sound (f). Because Image1 is an image with music, it has three elements (a, b, c). Three elements mean that Image1 can be played or not, and it has only music data. Both Video2 and Video3 are scenes that anchorpersons present, so they have elements (a, b, d). If three multimedia objects are replayed at once, music and speech sound can be played at the same time. Because we cannot understand the contents if two or more speeches
Figure 10: Constraint Network.
5.3 Algorithm We use a CSP algorithm considering search problem method [7]. Let us consider the following algorithm: 1. If all variables Xi (i = 1; : : : ; n) are instantiated, algorithm nishes this process and returns solution of CSP. If not, it goes to (2).
2. Algorithm propagates constraints with the way of forward checking [8].
News (Video2)
3. The next variable is selected from a set of unallocated variables, for deciding on good ordering (variable ordering).
Comment Screen Japanese Crested Scientific Name: Nipponia Nippon Distribution: Southeast Asia Total: 76 cm
4. Algorithm makes the choice of next value for the variable, which is selected in the process (3) (value ordering). 5. When a dead-end occurs, algorithm backtracks. However, it has solutions, selects one of them, and goes to (1). 6. Algorithm includes new allocated value for current solution, and makes this state a new search start point. It goes to (1) and repeats in the rest of search. The algorithm cannot avoid backtracking scheme, so that it is important to determine good heuristics in processes (3) and (4) to search eÆciently. As heuristics in variable ordering, system uses \emergency," which is predictively calculated as the occurrence of backtracking by the value allocation. That is, when one value can be allocated to selected variable, the algorithm calculates the possibility that the value con icts other values. In value ordering, the algorithm uses variable utility, which is evaluated predictively as the in uence of unallocated other values when the algorithm allocate certain value to selected variable. In other word, the algorithm evaluates the possibility when solutions can be opened from the current search situation. Let us consider the example of \audio" constraint by using this algorithm. We let variables be multimedia objects Image1, Video2, and Video3, and domain be elements (a, b, c, d, e, f). Each variable has constraints: p1 : (Image1, Video2) 2 (a, a), (b, b), (a, b), (b, a) p2 : (Video2, Video3) 2 (a, b), (b, a) p3 : (Video3, Image1) 2 (a, a), (b, b), (a, b), (b, a) If a variable Image1 is selected from three variables, a is selected for value of Image1 by the rst constraint p1 . Then, the value of Video2 is de ned b because p1 has an element (a; b). A variable Video3 is not allocated in this point. Accordingly, the algorithm goes to step (2), and repeats the same process. value for Video3 is selected a by the second element (b; a) in the second constraint p2 . This solution (Image1, Video2, Video3) = (a; b; a) is consistent to all three constraints. In short, sound of Video2 is not replayed, and music of Image1 and speech of Video3 are played at the same time. That is, it is solution of this CSP.
An anchor person (Video3)
Title (Image1)
Map
Figure 11: Demonstration of Multimedia Presentation.
In the same way, system would solve CSP about each of users' requirements. The CSP algorithm satis es each requirements, and multimedia presentation is created from this user-speci ed scenario. Figure 11 shows a layout example of multimedia objects in presentation. With explanation of the news and map, people can obtain many information.
6 Related Works Di erent approach has already been suggested by Hakkoymaz et.al. [9]. The following is a summary of the way for presentation. The system organizes concurrent presentations of selected segments by using inclusion and exclusion constraints. Three kinds of constraints occur when users specify a set of segments for a presentation. Two segments are sequentially represented (a sequentializer constraint). Some segments may be splited into two or more stream (a splitter constraint), and they will be merged into one stream (a merger constraint). In their research, the play order of segments is represented in a presentation graph by using these constraints. Hakkoymaz considered only two points: the length of the presentation and the number of windows to express a presentation organization. As for their research, the purpose of presentation organization constraints is to automate the organization of a concurrent presentation containing the selected multimedia objects. Therefore, they cannot deal with the overlap of the audio when videos are played at the same time. Semantic aspect of presentation organization must be considered, when constraints occur between multimedia objects. Although they have not studied the whole time length of the presentation and the number
of the windows, the overlap of the audio, and a layout on the screen. Therefore, we have proposed a mechanism of creating multimedia presentation in which multimedia objects are presented for the contents and the organization by using the idea of CSP.
7 Future Work We have studied the organization of multimedia presentation with syntactic and semantic aspects. In order to share, store, reuse information, we will apply XML (Extensible Markup Language) [5] as a format to capture and characterize multimedia information. One important property of XML for representing multimedia data is its ability to de ne speci c tag as required. Moreover, XML context rules are highly customizable through de nition in the DTD (Document Type Definition). Therefore, system can manage and store an enormous of structured data eÆciently, not spoiling syntactic and semantic aspects. For example, we describe scenario by using tag, such as \,"\," and so on. In this case, we can understand an anchorperson easily by detecting \" tag. In addition, people think that XML is appropriate to standard way of current digital broadcasting, so that we can make use of digital data on broadcasting, and retrieve and collect data. SMIL (Synchronized Multimedia Integration Language) has a wide range of features for putting multimedia presentations on the Web. For example, by using SMIL, audio is played after video has nished, and audio is played in parallel with image. SMIL can express such information with simple XML elements. Authors can describe scenario as SMIL documents for multimedia presentation. NHK Science and Technical Research Laboratories propose TVML (TV program Making Language) [10][11]. The system can produce a TV program in real time using CG. By making a text-based TVML script, a TVML player interprets this script and generates a TV program automatically in real time. As a TV-program metaphor, TVML can express multimedia presentation.
8 Conclusion In this paper, we have proposed the way to create multimedia presentation based on CSP from scenario temporal speci cation, which considers temporal relations between multimedia objects. In order to create user-speci ed presentations, system should satisfy users' requests, and consider the cooperation of some multimedia objects. However, constraints arise be-
tween multimedia objects. We treated this problem as CSP. Furthermore, with the easy slider manipulation on graphical user interface, users can decide the order of multimedia objects from certain video stream easily, and our system creates their requested presentation automatically. That is, certain video stream has many various presentations, which have di erent order of objects, layout on display, the length of playing, and so on. We will examine presentation creation mechanism that users see presentation more easily. If users cannot see over two videos at the same time, a video in studio and a live video may be limited. If so, a studio video is played in a small size window or not displayed. Then, system may provide much more other information to users.
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